Packed with vegetables, ratatouille is the perfect French dish for summer. Try this recipe for a simple and delicious lunch or dinner

Ratatouille is a healthy, colourful recipe perfect for the height of summer when all of the vegetables are at their peak.

Originally a way of using an abundance of vegetables in the simplest possible way, ratatouille roughly translates as mish-mash, and few farmers would have had time to sweat over each ingredient.

As a general rule, equal quantities of each vegetable – tomatoes, peppers, onions, courgettes and aubergines – works well, although I prefer a smaller amount of onion and use red rather than brown to add an extra colour.

For me, there is just one compromise that is not worth making. Ratatouille depends on the ripest, sweetest tomatoes, which need to be cooked down to concentrate their juices and flavour: a watery ratatouille is always disappointing.

The aubergines are hardest to get right because of their tendency to soak up oil: I let them cook for a minute of two in a small amount on oil, then drizzle in a little extra as needed, tossing the aubergines until they look glossy.

Fresh basil and garlic are a must and I often drizzle my ratatouille with pistou (the local pesto) for an extra blast of flavour.

In Nice, the home of this dish, the generally accepted method is to sauté each vegetable separately in olive oil and assemble them at the end, which guarantees that each one retains its colour, flavour and texture. However, one Michelin-starred chef told me that he added them one by one in very small cubes to the same pot (first the peppers, followed by the aubergines, courgettes and tomatoes) before slowly simmering them for an hour to reduce the liquid.

How to cut the vegetables is also open to interpretation: I prefer small dice but slightly larger dice is the norm and some people like to cut them into strips or rounds, like their mothers or grandmothers might have done.

1. Cut the tomatoes into quarters and place them in a heavy saucepan with a pinch of sugar and a pinch of salt. Bring to the boil and cook over medium heat for 30-40 minutes, until most of the liquid has evaporated and the sauce has thickened. Strain through a food mill or large-holed sieve to remove the skins.

2. Cut the yellow and red peppers, aubergines and courgettes into 1cm dice and sauté them one at a time on medium-high heat with a little salt in about 1tbsp olive oil for each different type of vegetable (the aubergines might need a little more during cooking). When the vegetables are soft and lightly browned but not mushy, set them aside in a large bowl (they can be combined at this point).

3. Heat 1tbsp olive oil in a sauté pan, sweat the red onion and garlic over a medium heat for a few minutes until lightly caramelised, and add the strained tomatoes. Add all the vegetables and the chopped basil and stew gently for five minutes. Season with salt and chili pepper to taste.

4. For the pistou, blend all the ingredients in a food processor.

5. Just before serving, spread the ratatouille over the slices of pain de campagne and drizzle with pistou (or serve it on the side).